The proposed studies are intended to provide new information of clinical importance on the functional consequences of restricted injuries to peripheral nerves or the spinal cord. These experiments are conducted with non-human primates, because the organization of the peripheral nerves and spinal pathways of primates differs considerably from that of other mammals. The injuries are restricted to an individual nerve with a small peripheral distribution or to a single spinal pathway, so that non-debilitating models can reveal important principles that will aid in the diagnosis, management and treatment of the more severe injuries that are seen clinically in the human population. In addition, we will apply new techniques for increasing the resolution of nuclear magnetic resonance (NMR) imaging to evaluate spinal cord injuries, which will greatly enhance the ability to correlate functional deficits with the location and extent of a lesion. Two sets of studies will evaluate sensory capacities that are diminished or remain after interruption of the dorsal column pathway on one side of the spinal cord. The first of these will provide the first thorough series of tests of proprioceptive sensations (providing information about the movement and position of the limbs) following a lesion of this pathway. The results of this study will provide needed information concerning mechanisms of motor deficits that occur with spinal injuries. Also, the effects of dorsal column lesions on tactile sensitivity will be investigated. Previous studies have indicated that some difficulties with touch sensations result not from a loss of the necessary information but from an inhibitory process that is released by the lesion. Further understanding of this inhibitory process may suggest strategies to circumvent it, for the purpose of restoring tactile capabilities. Two other sets of studies are concerned with alleviation of pain following injuries to peripheral nerves. The first of these investigations seeks to reveal why partial injuries to peripheral nerves sometimes result in a perception of pain in the region innervated by that nerve. If the mechanism for generation of this abnormal sensation can be determined, then treatments of peripheral nerve injuries for prevention of pain could be developed. These studies take advantage of leads that have recently come from rodent models. Another investigation seeks to reveal reasons for return of pain sensitivity after it is very effectively reduced by a spinal cord lesion (anterolateral chordotomy) that has been used extensively to control intractable pain in human patients with cancer. Identification of the mechanisms for this recovery could lead to improved surgical treatments for control of chronic pain. The stimuli utilized in these studies are brief, non-injurious and easily tolerated by monkeys and humans. This is a multidisciplinary approach within the Neurosciences, involving direct correlations of anatomical and physiological data with highly quantitative evaluations of sensory and motor reactions to precisely controlled somatosensory stimuli.